1. Field of the Invention
The invention relates to iron-boron glassy metal alloys having improved as-cast filament strength resulting from substitution of iron by molybdenum.
2. Description of the Prior Art
Glass forming metal alloys are conveniently processed in filamentary form by casting and rapid quenching of the melt using processing techniques that are now well-known in the art. The term "filament" is used herein to represent a slender body whose transverse dimensions are much less than its length. In the present context, the filaments may be ribbons, sheets, wires and the like of regular or irregular cross-section.
Glassy metal alloys in wire form have been disclosed in U.S. Pat. No. 3,556,513, issued Dec. 24, 1974 to H. S. Chen et al. These glassy wires have a composition of about 70 to 87 atom percent of at least one transition metal and about 13 to 30 atom percent of at least one element selected from the group consisting of phosphorus, boron, carbon, aluminum, silicon, tin, germanium, indium, beryllium and antimony.
Binary glassy metal alloys consisting essentially of about 75 to 85 atom percent iron or cobalt and 15 to 25 atom percent boron have been disclosed in application Ser. No. 636,323, filed Nov. 28, 1975, now U.S. Pat. No. 4,036,638, issued July 19, 1977. The iron-boron alloys are disclosed as having intrinsic strengths of about 470 to 610 kpsi.
As is well-known, intrinsic strength is measured by hardness and/or tensile testing of carefully polished specimens. For example, in Vol. 9, Scripta Metallurgica, pp. 431-436 (1975), it is shown that hardness values determined by a Vickers diamond pyramid indenter can be converted to yield strength, employing a dimensionless conversion factor of about 3.2. However, tests of filaments of the binary iron-boron glassy metal alloys in the as-cast state have invariably exhibited substantially lower tensile strength than the intrinsic alloy strength observed in carefully polished specimens. It appears that filament casting methods may subject the alloy to processing instabilities which are manifested as rough edges and surfaces on the as-cast filaments.
As used herein, the term "as-cast" refers to the state or condition of a filament as it is processed by the casting apparatus. More specifically, the term excludes polishing of the filament, as by mechanical or electrochemical techniques.